Devices used to follow the penetration of an instrument in an anatomical structure, in particular, a bone structure are known.
Ep 0 607 688 describes a procedure and system for the insertion of a pedicular vertebral screw, including applying an electric potential to the surface of the cavity, and observing the muscular reactions provoked by this stimulation.
It is also known to measure the modification in the impedance of the region neighboring the explored bone cavity using a sound presenting an electrode coming into contact with the wall of the bone cavity, and a second electrode placed on the patient. The purpose is to detect the gaps in bone matter, for example, during an operation preparing for the insertion of a pedicular screw in a vertebra.
The information gathered with such an approach is difficult to interpret since the impedance measured between the two electrodes is perturbed by artifacts related to the variation in the penetration of the sound in the cavity. The resistivities of the air, muscle tissue, bone tissue and gaps differ, and the signal measured is the result of several parameters that in part mask the useful information corresponding to the passage of the electrode of the sound near a gap.
In addition, the device is not very practical since it first requires calibration (reference related to soft tissue). Finally, such a device remains not very easy to manipulate due to the presence of external cables.
It could therefore be advantageous to provide a device whose output signal is not disturbed by variations due to the depth of the entry of the penetration instrument.